The invention relates to double metal cyanide (xe2x80x9cDMCxe2x80x9d) complex catalysts which are especially useful in the polymerization of epoxides and show significant activity. The invention further is directed to methods for preparing such DMC catalysts.
DMC compounds are known catalysts for epoxide polymerization. Conventional DMC catalysts are prepared by reacting an aqueous solution of a metal salt and metal cyanide salt to form a precipitate of the DMC compound. The catalysts are highly active and are especially useful in the production of polyether, polyester, and polyetherester polyols having low unsaturation. Many of such polyols are useful in the production of polyurethane coatings, elastomers, sealants, foams, and adhesives.
DMC catalysts were disclosed over 30 years ago by General Tire. U.S. Pat. No. 3,427,256 discloses a composition containing two metals selected from a wide variety of metals along with an organic complexing agent selected from an ether with only ether functionality, a sulfide with only sulfide functionality, an amide with only amide functionality and a nitrile with only nitrile functionality wherein the complexing agent serves to activate the catalyst. This patent also discloses a method for washing the DMC with the organic complexing agent. U.S. Pat. No. 3,427,334 discloses DMC compositions containing the same metals set forth in U.S. Pat. No. 3,427,256 with organic complexing agents selected from alcohols with only hydroxyl functionality, aldehydes with only aldehyde functionality, ketones with only ketone functionality, and methods for the washing and drying of the catalyst. U.S. Pat. No. 3,427,335 discloses DMC compositions containing, as the organic complexing agent, ethers which also may contain halogen, esters with only ester functionality, cyclic ethers with only cyclic ether functionality, and methods for precipitating the catalyst and washing and drying it. U.S. Pat. No. 3.404,109 discloses a DMC catalyst composition of formula Zn3[Co(CN)6]2 .1.7 glyme .1.2 H2O .1.2 ZnCl2. This gives a mole fraction Zn/Co of 2.1. In each of these patents, the DMC is first precipitated without organic complexing agent followed by washing with a complexing agent/water mixture. General Tire further describes similar DMC/glyme catalysts in several research articles published in the open scientific literature. See, for example, R. J. Herold et al., Polym. Prepr., Amer. Chem. Soc., Div. Polym. Chem., xe2x80x9cHexacyanometallate Salt Complexes for Epoxide Polymerizationxe2x80x9d (1972) 13(1), 545-550, discussed in further detail below.
U.S. Pat. Nos. 4,477,589 and 4,472,560 disclose DMC catalyst compositions and a process for polymerizing epoxides with such catalysts, respectively. This improved DMC technology is also discussed in a research paper. See J. Kuyper et. al., J. Catal, xe2x80x9cHexacyanometallate Salts Used as Alkenexe2x80x94Oxide Polymerization Catalysts and Molecular Sieves,xe2x80x9d (1987), 105(1), 163-174, discussed in detail below. The compositions of the DMC and associated organic complexing agents in the ""560 patent are similar to those described in t he patents of the preceding paragraph and further include, as additional complexing agents or activators, an acid such as HCl and a salt, such as ZnSO4, generally added to the reactor with the DMC catalyst just prior to polymerization. U.S. Pat. No. 4,477,589 discloses an acid modified DMC prepared initially without organic complexing agent, followed by the addition of sodium hydroxide to form the intermediate hydroxide salt, isolation, and lastly neutralization by HCl with and without glyme organic complexing agent. In both patents, the ethers or glymes are the preferred organic activating agent. These patents further disclose the use of Zn and Co in the presence of glyme, HCl, and ZnSO4.
A method where the DMC catalyst is precipitated in the presence of the organic complexing agent, is also taught later in a Japanese Patent (JP 4,145,123) and in U.S. Pat. No. 5,712,216. Japanese Patent JP 4,145,123 teaches DMC catalysts coordinated with tert-butanol, prepared by stirring an aqueous solution containing zinc chloride, potassium cyanocobaltate, and the tert-butanol ligand. This catalyst had a substantially improved catalytic life over the DMC/glyme catalyst.
U.S. Pat. No. 5,158,922 discloses an improved process for making easily filtered DMC catalysts by controlling the order of reagent addition, the reaction temperature, and the stoichiometric ratio of the reactants. This patent teaches the use of at least about a 100% stoichiometric excess of the metal salt relative to the metal cyanide salt and glyme, as organic complexing agent. Zinc hexacyanocobaltate catalysts prepared by this procedure generally have zinc chloride to zinc hexacyanocobaltate molar ratios of about 0.6 or more; i.e., a mole fraction Zn/Co greater than 1.8. It further discloses compositions having as little as 0.2 moles of metal salt per mole of DMC compound (Zn/Co=1.6). While the procedure described in the ""922 patent (large excess of zinc chloride) works well with glyme, it is stated in U.S. Pat. No. 5,627,122 that this excess is less satisfactory for use with other complexing agents, including tert-butyl alcohol. When tert-butyl alcohol is used, the catalyst precipitate becomes gelatinous and difficult to isolate. In addition, the activity of these catalysts for epoxide polymerizations, although high compared with KOH catalysts, is still somewhat less than desirable.
U.S. Pat. Nos. 5,470,813 and 5,712,216 disclose improved methods for making DMC catalysts in the presence of an organic complexing agent, preferably t-butanol. The ""813 Patent uses a homogenization method wherein a water soluble metal salt is intimately mixed with a water soluble metal cyanide salt. The homogenizer used is not described. In the examples, t-butanol, as complexing agent, is slowly added after the other salts are mixed. Contrasting examples with xe2x80x9cnormalxe2x80x9d mixing fail to show the same activity. U.S. Pat. No. 5,712,216 discloses a method where the organic complexing agent is initially present in the reactant solutions, eliminating the need for homogenization. Here, all of the included examples only show data for reduced unsaturation, with no demonstration of improved activity.
U.S. Pat. Nos. 5,482,908 and 5,627,120 teach improvement of the activity of the DMC catalyst by the use of two complexing agents. The first complexing agent, in an amount of from 5 to 80 wt. %, is a polyether polyol. U.S. Pat. No. 5,482,908 covers polyols having a number average molecular weight of greater than 500 Da (preferred is poly(propylene oxide) polyol with molecular weight between 2,000 and 4,000). U.S. Pat. No. 5,627,120 covers polyols having a number average molecular weight less than 500 Da, and may contain, as polyol activator, the monomethyl ether of tripropylene glycol with t-butanol. In each case, the second organic complexing agent is t-butanol. A stated advantage is the reduction of Co and Zn in the final polyol, reported to be xe2x89xa65 ppm.
Companion patents include U.S. Pat. Nos. 5,589,431 and 6,018,017. U.S. Pat. No. 5,589,431 discloses a method for producing polyols and compositions of matter for polyols produced with the catalysts of U.S. Pat. No. 5,470,813. U.S. Pat. No. 6,018,017 discloses polyols as being limited to triols and higher functionality polyols, produced from the catalysts of U.S. Pat. No. 5,712,216.
U.S. Pat. No. 5,627,122 discloses a xe2x80x9ccrystallinexe2x80x9d DMC complex catalyst which comprises a DMC compound, an organic complexing agent, and a metal salt, wherein the catalyst contains less than about 0.2 moles of the metal salt per mole of DMC compound; i.e., mole fraction Zn/Co less than 1.6. Organic complexing agents include alcohols, aldehydes, ketones, ethers, esters, amides, ureas, nitrites, sulfides, and mixtures thereof. With low levels of ZnCl2, these catalysts are very active and reportedly produce polyols with very low unsaturation. WO 99/19063 discloses a xe2x80x9csubstantially crystallinexe2x80x9d DMC catalyst that incorporates a normal complexing agent, such as t-butanol, and a functional polymer such as a polyether, a polyester, a polycarbonate, and similar functional polymers. The ZnCl2 content is greater than 0.2 mole/mole of DMC (Zn/Co greater than 1.6). Polyols produced from these crystalline DMC catalysts have low unsaturation, lower than 0.01 meq/g.
Polyol activators are further disclosed in WO 99/19062 (polyester activator), WO 99/33562 (polycarbonate activator) and WO 99/46042 (polyethylene oxide polyol modifier with a molecular weight greater than 500). Additional patents, WO/0007720, WO/0007721, WO/0015336, WO/0015337, WO/0047649, WO/0047650, and U.S. Pat. No. 6,204,357 disclose a DMC catalyst containing t-butanol further modified with a secondary complexing agent of an alkyl glucoside, a glycidol capped polyol, a polyalkylene glycol sorbitan ester, a polyvalent carboxylic acid ester, a bile acid ester or amide, or an ionic surface or interface active compound, and one or more cyclodextrins, respectively.
U.S. Pat. No. 5,545,601 discloses a DMC catalyst containing t-butanol modified with a polyol having tertiary alcohol end groups. The tertiary end group polyols are stated to improve catalyst activity and maintain low unsaturation at higher polymerization temperatures.
U.S. Pat. No. 5,714,428 discloses DMC catalysts modified with other functional polymers such as a polyester, a polycarbonate, an oxazoline, a polyalkylenimine, a maleic acid or maleic anhydride copolymer, hydroxyethyl cellulose, starches and polyacetals in addition to t-butanol. Furthermore, U.S. Pat. No. 6,013,596 discloses cyclic bidentate complexing agents such as lactones or lactams in addition to t-butanol.
Catalyst modifications are further disclosed in U.S. Pat. No. 5,693,584 which is directed to the addition of an organo phosphine oxide to a DMC catalyst in order to maintain low unsaturation even where propoxylation is carried out at higher temperatures. The companion to this patent, U.S. Pat. No. 6,211,330, covers the process to make epoxide polymers form this catalyst. Moreover, U.S. Pat. No. 5,952,261 discloses a composition and method to prepare a DMC catalyst modified with Group IIA compounds, such as CaCl2. In addition, protic acid DMC modification, disclosed in WO 09966874, non-protic acid DMC modification, disclosed in U.S. Pat. No. 6,028,230, and silylated modified DMC catalysts disclosed in U.S. Pat. No. 6,051,680, claim to eliminate the high molecular weight tail that is prevalent with DMC polymerizations.
WO 99/16775 discloses a crystalline DMC catalyst in which the standard ZnCl2 is replaced with zinc formate, acetate, or propionate and the organic complexing agent is broadly defined as alcohols, aldehydes, ketones, ethers, esters, amides, ureas, nitriles, and sulfides.
As discussed above, DMC catalysts are usually prepared in the presence of a low molecular weight organic complexing agent, typically an ether such as glyme (1,2-dimethoxyethane) or diglyme. The complexing agent favorably impacts the activity of the catalyst for epoxide polymerization. Other known complexing agents include alcohols, ketones, esters, amides, and ureas. As disclosed in Japanese Patent JP 4,145,123 and in U.S. Pat. No. 5,470,813, preparations of DMC catalysts with water-soluble aliphatic alcohol complexing agents, such as tert-butyl alcohol, are widely used. DMC catalysts are normally produced with an excess of the metal salt compared with the amount of metal cyanide salt as set forth in U.S. Pat. Nos. 3,427,256, 3,278,457, and 3,941,849.
The structures of DMC catalysts are not well understood. Recently, four patents, discussed abovexe2x80x94U.S. Pat. Nos. 5,470,813; 5,712,216; 5,482,908; and 5,627,120xe2x80x94stated that the improved activity of DMC catalysts was attributed to the DMC catalysts being xe2x80x9csubstantially amorphousxe2x80x9d, in spite of powder x-ray diffraction that showed otherwise. Additionally U.S. Pat. Nos. 5,627,122 and WO 99/19063 characterized DMC catalysts with improved activity as being xe2x80x9csubstantially crystalline.xe2x80x9d Applying the teachings of U.S. Pat. No. 5,712,216 to the xe2x80x9csubstantially crystallinexe2x80x9d Catalyst A of WO 99/19063 would lead to the incorrect conclusion that the xe2x80x9csubstantially crystallinexe2x80x9d Catalyst A of WO 99/19063 is approximately 40% crystalline and 60% amorphous (based on XRPD).
Contrary to the teachings set forth in U.S. Pat. Nos. 5,470,813; 5,712,216; 5,627,120; and 5,482,908, as well as WO 99/19062, amorphous DMC catalysts have not yet been discovered. Many DMC catalysts are poorly understood based on their powder X-ray diffraction (XRPD) patterns, and, as discussed above, have been incorrectly characterized as being xe2x80x9camorphousxe2x80x9d or xe2x80x9csubstantially amorphousxe2x80x9d. Amorphous materials, including amorphous catalysts, exhibit no more than two or three broad XRPD peaks (xe2x80x9cmaximaxe2x80x9d). In order for an amorphous structure to exist, the atomic structure would need to exhibit either no periodicity or no long-range order. Thus, to date, all claims of amorphous DMC catalysts are either false or unsubstantiated.
FIG. 1 shows a XRPD pattern that we took for amorphous silica, using the experimental setup later described as the second XRPD method. Relative to other XRPDs shown herein, the intensity axis shown in this XRPD is highly magnified. This XRPD pattern can be compared against a pattern given for amorphous silica in the book by Snyder and Jenkins xe2x80x9cIntroduction to X-ray Powder Diffractometryxe2x80x9d, Wiley-Interscience, 1996, page 25.
Characteristically, the first peak in an amorphous silica pattern should be the largest. This is the peak labeled xe2x80x9c2xe2x80x9d, occurring at about 23 degrees two-theta. The peak labeled xe2x80x9c3xe2x80x9d at 43 degrees two-theta shows up only on higher magnification, and is also associated with amorphous silica. The peak labeled xe2x80x9c1xe2x80x9d (14 degrees two-theta) appears to belong to another amorphous material, perhaps the amorphous kapton film used in wrapping this sample (under normal magnification, this would not show up; kapton film was not used for any other PXRD patterns contained herein). The increase in intensity for two-theta  less than 10 degrees is due to air scatter in this highly-magnified pattern. The sharp peak labeled xe2x80x9cixe2x80x9d occurring at about 28 degrees two-theta is due to a crystalline impurity either in the sample or in the sample holder. This impurity represents well less than 1 weight percent of the sample.
As set forth in FIG. 1, amorphous materials, including amorphous catalysts, exhibit no more than two or three broad XRPD peaks (xe2x80x9cmaximaxe2x80x9d). In order for an amorphous structure to exist, the atomic structure would need to exhibit either no periodicity or no long-range order. Thus, to date, all claims of amorphous DMC catalysts are either false or unsubstantiated.
FIG. 1 and FIG. 2 show XRPD for crystalline DMC compounds from U.S. Pat. Nos. 5,712,216; 5,714,428; and 5,627,122. In contrast to amorphous structures, the XRPD for crystalline materials demonstrate near-zero intensity except for sharp maxima [B. D. Cullity and S. R. Stock, Elements of X-ray Diffraction, 3rd Ed., (Prentice Hall, Upper Saddle River, N.J., 2001)]. For instance, the sharp peak at about 28xc2x0 2-theta in FIG. 1 is due to a crystalline impurity in the amorphous silica sample.
The structural form of a material can be determined by the nature of the XRPD peaks, including their positions, intensities and widths. Widths are determined as full width at half maximum (FWHM)), and are dependent on the wavelength (xcex) of the X-ray source. [When used herein, values of FWHM are for Cu Ka radiation (xcex=1.54 xc3x85)]. For perfect crystals, XRPD resolution is limited by the diffractometer (perfectly sharp scattering). Typically, FWHM  less than 0.3xc2x0 2-theta. For imperfect (defective) crystals, and also for very small crystals (domains less than 500 xc3x85), the peaks are broadened, with 0.3 less than FWHM less than 4xc2x0 2-theta. Peak broadening can also be due to a variety of effects, including crystallite size, defects and structural disorder. For liquids and amorphous solids (glasses), the XRPD intensity is a continuous, slowly varying function with only a few broad maxima, each of which has a FWHM typically exceeding 4xc2x0 2-theta. For these cases, the atomic structure exhibits no periodicity or long-range order. In FIG. 1, the sharp peak due to the crystalline impurity (labeled xe2x80x9cixe2x80x9d) has FWHM=0.12xc2x0 2-theta, and the main peak due to amorphous silica (labeled xe2x80x9c2xe2x80x9d) has FWHM greater than 8xc2x0 2-theta. For the XRPD pattern for amorphous silica in Snyder""s text book, the main peak has FWHM greater than 12xc2x0 2-theta.
The DMC catalysts of FIGS. 1 and 2 are considered to be imperfect crystals, except for the cubic DMC of FIG. 2, which appears to be a very small crystal. Some crystalline DMC catalysts, as shown in FIGS. 1 and 2, have broad peaks (FWHM roughly 2xc2x0) at roughly 14 and 18xc2x0. In such DMC catalysts, these broad peaks are associated with a relatively sharp peak at about 23.6xc2x0. An amorphous DMC catalyst would have very broad peaks (FWHM greater than 4xc2x0) that are not associated with any sharp peaks. The DMC catalysts of FIGS. 1 and 2 are crystalline. Some of these catalysts may be poorly crystalline, but they are not amorphous. For the DMC catalysts shown in FIG. 2, the observation of twelve separate diffraction peaks, many with FWHM less than 2xc2x0, indicates that these DMC catalysts are crystalline, not amorphous.
The characterization of the DMC catalyst in U.S. Pat. No. 5,712,216 as xe2x80x9csubstantially amorphousxe2x80x9d, i.e., xe2x80x9csubstantially noncrystalline, lacking a well-defined crystal structure, or characterized by the substantial absence of sharp lines in the X-ray diffraction (XRD) patternxe2x80x9d (1. 66, col. 3-1. 3, col. 4) is thus technically incorrect. Further, the PXRD patterns for three different DMC catalysts using t-BuOH as complexing agent differ very little (see FIG. 2). Take, for instance, the PXRD labeled as xe2x80x9cU.S. Pat. No. 5,712,216 25% cubicxe2x80x9d. In U.S. Pat. No. 5,712,216, this catalyst is described as xe2x80x9csubstantially amorphous, 25% crystallinexe2x80x9d. The PXRD for this catalyst is essentially identical to that labeled as xe2x80x9cU.S. Pat. No. 5,712,216 Comparative Example 3 [Asahi]xe2x80x9d, and is very similar to that labeled xe2x80x9cU.S. Pat. No. 5,627,122 Example 1xe2x80x9d (and described therein as substantially crystalline). In fact, all five of the DMC catalysts illustrated in FIG. 2 have varying amounts of two crystalline phasesxe2x80x94cubic and a second phase (xe2x80x9cU1xe2x80x9d)xe2x80x94with the proportion of cubic phase dropping from greater than 99 weight percent to less than 1 weight percent. The U1 DMC crystalline phase of FIG. 2 is defined as having a combination of three peaks, as follows.
1. A sharp peak at 23.64xc2x10.32 deg 2-theta [d=3.76xc2x10.05 xc3x85], with width FWHM less than 0.45 deg 2-theta.
2. A broad, asymmetric peak with a maximum at about 14.3xc2x10.7 deg 2-theta [d=6.20xc2x10.30 xc3x85], rising sharply at low angle, and falling gradually at high angle, with width FWHM=1.5xc2x10.6 deg 2-theta.
3. A broad peak with a maximum at about 18.4xc2x11.1 deg 2-theta [d=4.84xc2x10.30 xc3x85] with width FWHM=1.6xc2x10.8 deg 2-theta. This peak can also be asymmetric; in some cases rising gradually at low angle and falling sharply at high angle.
Two of these features are included as claims in U.S. Pat. No. 5,470,813 (xe2x80x9cArco substantially amorphousxe2x80x9d): claim 24. xe2x80x9c(d-spacing, angstroms): 4.82 (br), 3.76 (br)xe2x80x9d [where br means broad]. All three features are present in the catalysts shown in FIG. 1 from this and subsequent patents from the assignee (U.S. Pat. Nos. 5,712,216 and 5,714,428). In addition, all three of these features are included in Table 1 of WO 99/19063. If the U1 crystalline phase is present, the XRPD contains all three of the above features, as shown in the top two XRPD of FIG. 3 for a DMC/t-BuOH/polyester catalyst (XRPD from WO 99/19063) and a DMC/t-BuOH/poly-PO catalyst:
Cases that contain the sharp peak (23.6 deg 2-theta) plus broad, poorly-resolved features between 13.5 and 22.5 deg 2-theta are called U1A [see FIG. 3, bottom XRPD, for an alternative DMC/t-BuOH/poly-PO catalyst, and FIG. 5 herein, and FIG. 6 of U.S. Pat. No. 5,712,216]. U1A is related to U1, and its characteristic X-ray pattern can occur from a merging of peaks 2 and 3 due to a variety of factors taken singly or in combination, such as a narrowed splitting, increased asymmetries, and increased FWHM values. XRPD for DMC catalysts that contain either U1 and/or U1A crystal phases are given in FIGS. 1-3.
The difficulty in characterization of the structural forms of DMC catalysts was earlier recognized with those catalysts containing glyme as complexing agent. For instance, in R. J. Herold et al., Polym. Prepr., Amer. Chem. Soc., Div. Polym. Chem., xe2x80x9cHexacyanometallate Salt Complexes for Epoxide Polymerizationxe2x80x9d (1972) 13(1), 545-550, the authors describe DMC/glyme catalysts as xe2x80x9clargely amorphousxe2x80x9d. On the other hand, J. Kuyper et. al., J. Catal, xe2x80x9cHexacyanometallate Salts Used as Alkenexe2x80x94Oxide Polymerization Catalysts and Molecular Sieves,xe2x80x9d (1987), 105(1), 163-174, describe DMC/glyme catalysts as crystalline by giving xe2x80x9cfairly simple line patterns. Depending upon the preparative conditions (particularly during the isolation of the solid catalyst), at least three different, though similar, diffraction patterns are obtained. Unfortunately, no assignment of cell parameters was found.xe2x80x9d Both of these references fail to provide XRPD data. Kuyper reported that attempts to index the XRPD were unsuccessful. The detailed crystal structure of the DMC/glyme catalyst of Kuyper remains unknown; to date the unit cell parameters and atomic coordinates have not been published.
As part of the work described herein, several DMC/glyme catalysts were synthesized using procedures set forth both in Kuyper (Shell) and also in Herold (General Tire). The XRPD for these catalysts were measured (a typical case is set forth as the lowermost XRPD in FIG. 4). Surprisingly, Shell DMC/glyme procedures (using HCl) and General Tire DMC/glyme procedures (using acid ion exchange) were identified that gave catalysts that have nearly identical XRPD patterns; i.e., both give the XRPD pattern shown at the bottom of FIG. 4. In addition, this XRPD pattern is very similar to that shown in U.S. Pat. No. 5,712,216 (Arco; see FIG. 2 of this patent), termed as a xe2x80x9cconventional DMC catalystxe2x80x9d. Computational indexing of the XRPD pattern was carried out using commercial software [MDI Jade software for pattern analysis and phase identification; http://www.materialsdata.com/products.htm]. Computational indexing requires that either the sample is a single crystalline phase, or that overlapping multiphase peaks (as shown in FIG. 4) can be separated into peaks for separate crystalline phases. For selected DMC/glyme catalysts, no substantial impurity peaks could be identified from multiple samples using standard techniques (see Cullity, Chapter 9). As determined by PXRD, the DMC/glyme catalyst of FIG. 4 does not contain any detectable amounts of the known cubic DMC (hydrated) or rhombohedral DMC (dehydrated) crystal phases (see below), nor does it contain any detectable amount of U1 or U1A. Using Jade, the peaks for this catalyst were indexed to a monoclinic unit cell with cell parameters (a, b, c)=(12.85, 7.61, 9.84 xc3x85); xcex2=107.6 xc3x85.
Of interest, the XRPD pattern in FIG. 4 for the DMC/glyme catalyst is similar to FIG. 2 of U.S. Pat. No. 5,712,216, termed as a xe2x80x9cconventional DMC catalystxe2x80x9d. WO 99/16775 further reports an additional crystalline DMC catalyst that is also monoclinic.
Hydrated cubic DMC of the prior art contains no excess Zn nor complexing agent. It has the formula Zn1.5Co(CN)6.6H2O. Hydrated, cubic DMC is set forth as the topmost XRPD in FIG. 4. Partially dehydrated DMC, illustrated as the middle XRPD in FIG. 4, also contains no excess Zn and consists of a mixture of cubic and rhombohedral phases. It has the formula Zn1.5Co(CN)6.xc3x97H2O, 1xe2x89xa6xxe2x89xa64. It may easily be made by simple variations of known procedures for making cubic DMC, such as by combination of starting materials, filtration and drying.
The difficulty in characterizing DMC catalysts was recently noted in WO99/16775 where the applicant states that xe2x80x9c[DMC catalysts] as a rule are hard to characterize by x-ray methods, not very crystalline and in part, also radiographically amorphous compounds, or crystalline . . . with a cubic structure.xe2x80x9d The applicant further claims a xe2x80x9ccrystalline monoclinic DMC catalystxe2x80x9d, as well as two additional crystalline DMC catalysts that are neither cubic, nor amorphous, nor well understood based on XRPD.
In summary, DMC catalysts have been described both as xe2x80x9camorphousxe2x80x9d and as xe2x80x9ccrystalline.xe2x80x9d In so doing, the term xe2x80x9camorphousxe2x80x9d has taken on an incorrect meaning as the XRPD pattern continues to be misunderstood or alternatively is too complicated to comprehend.
There exists a need for improved double metal cyanide catalysts, especially catalysts which are easy to prepare and isolate, and exhibit excellent polymerization activity. Further, such catalysts preferably render polyether polyols having a narrow molecular weight distribution and low unsaturation.
The invention relates to an improved double metal cyanide (xe2x80x9cDMCxe2x80x9d) complex useful as a catalyst in epoxide polymerization. The catalysts of the invention show significant activity for different types of crystal structures or mixtures of crystal structures. The invention further includes methods for preparing the novel complexes and the polyether polyol products produced therefrom. In particular, the catalysts of the invention render a polyol having low unsaturation.
The complexes are prepared by reacting an aqueous solution of a metal salt and a metal cyanide salt in the presence of the organic complexing agent. Preferred multifunctional complexing agents are those of the formula:
R1O(CH2CHR2O)xHxe2x80x83xe2x80x83(I)
and mixtures thereof, wherein:
x is 1, 2, or 3;
R1 is a C1-C4 alkyl group; and
R2 is xe2x80x94H or a xe2x80x94CH3 group.
Such multifunctional complexing agents render unnecessary any need for use of functionalized polymers as secondary complexing agents. Preferred multifunctional primary complexing agents are the glycol ethers, such as alkyl ether of propylene glycol (xe2x80x9cPGxe2x80x9d), dipropylene glycol (xe2x80x9cDPGxe2x80x9d), tripropylene glycol (xe2x80x9cTPGxe2x80x9d) and similarly the alkyl ethers of ethylene glycol (xe2x80x9cEGxe2x80x9d), diethylene glycol (xe2x80x9cDEGxe2x80x9d) and triethylene glycol (xe2x80x9cTEGxe2x80x9d). The term xe2x80x9calkylxe2x80x9d refers to methyl, ethyl, propyl, isopropyl, butyl, isobutyl, and t-butyl. In place of one or more alkyl groups in such complexing agent, a C6-C23 aryl group may further be employed. The choice of alkyl group may be determined by the miscibility of the complexing agent in water. Additionally, even polybutylene glycol derivatives with shorter chain alkyl groups for the ether are appropriate complexing agents.
Catalysts of the invention are DMC crystalline phases or mixtures of such phases, including monoclinic, orthorhombic, cubic, U1, and U1A crystalline phases, as determined by XRPD. Some of the catalysts contain no detectable amount of the cubic, U1, or U1A DMC crystalline phases.
Some of the catalysts contain a crystalline impurity of approximate composition Zn5(OH)8Cl2.H2O, known as simonkolleite. This impurity is believed to be catalytically inert. The match was made using the database from the International Centre for Diffraction Data (ICDD; see Cullity, Chapter 9). The impurity can be indexed to a hexagonal unit cell with approximate parameters (a,c)=(6.325, 23.60 xc3x85). These parameters are in good agreement with that reported for simonkolleite: (a,c)=(6.334, 23.58 xc3x85) and (6.34, 23.64 xc3x85). The assignment is confirmed by matching the intensity pattern. See: Hesse, F. R. G. Schmetzer, K.; Schnorrer-Koehler, G.; Medenbach, 0. Neues Jahrb. Mineral., Monatsh. (1985), (4), 145-54. CAN 102:223561 Wulfingite, epsilon-Zn(OH)2, and simonkolleite, Zn5(OH)8Cl2.H2O, two new minerals from Richelsdorf. Also see Allmann, R. Z. Kristallogr. (1968), 126(5-6), 417-26. CAN 69:90890 Refinement of the structure of zinc hydroxide chloride, Zn5(OH)8Cl2.1H2O.
An excess of the metal salt, as compared to the metal cyanide salt, is preferably used and the resulting DMC complex includes some of the metal salt. Typically, the DMC catalyst complex of the invention contains more than 0.2 mole of metal salt per mole of metal cyanide compound, for example Zn/Co greater than 1.6.
Such catalyst complexes exhibit excellent activity for polymerizing epoxides even where there is no secondary complexing agent. The catalyst activities are significantly higher than the activities available from conventional KOH catalysts, and are also higher than those of ordinary DMC catalysts.